Spark plugs



July 15, 1.958 w. HARPER, JR 2,843,780

SPARK PLUGS Filed Jan. 31, 1952 IN VEN TOR.

rmwdwly a United States Patent SPARK PLUGS William Harper, Jr., Huntington, N. Y.; Genevieve G. Harper, executrix of said William Harper, deceased, assignor to Jet Ignition Company, Inc., Larchmont, N. Y., a corporation Application January 31, 1952, Serial No. 269,232

Claims. (Cl. 313--143) This invention relates to spark plugs and aims to provide a spark plug having a longer life than those heretofore used. The greater durability of the spark plug gives it an important advantage for use in aviation engines and makes it desirable for use in other internal combustion engines.

The limiting factor in the life of a spark plug is the deterioration in the electrodes under the effect of excessive heat. The heat to which the electrodes are subjected comes mainly from two sources: (1) The heat of the spark itself which is proportional to the amperage of the spark, and (2) the heat of the hot gases in the cylinder which re-enter the spark plug. My invention provides a simple unitary device which reduces the heat from both of these sources and thus increases the life of the electrodes and, therefore, of the entire spark plug. a

A further object of my invention is to increase th efficiency of ignition, especially in starting.

In accordance with my invention, the two electrodes are located on the axis of the spark plug and each is provided with a convex spherically curved end. The gap between the electrodes is located in a constricted passage in the body of the spark plug. The outer end of this passage is closed by a head containing helical passages connecting with nearly axial jet passages of smaller cross-section. This construction reduces heating both during ignition and thereafter. During ignition the con stricted passage in which the gas is located contains a swirling mass of gas which draws the spark initiating at the center of the convex electrodes laterally outward, thus increasing its length and reducing its amperage and consequently its heating eifect on the electrodes. The lengthening of the spark also increases the efliciency of the ignition, especially in starting when the mixture is cold. After the burning gases have been ejected from the spark plug to ignite the fuel in the cylinder, return flow of the hot gases to the spark plug chamber is retarded and the gases are cooled by expansion so that the heating of the electrodes by the burning gases is reduced.

In order that my invention may be clearly understood, I will describe in detail the embodiments of it shown in the accompanying drawings, in which Fig. 1 is an axial section of a spark plug embodying my invention in a form which I now consider most desirable;

Fig. 2 is an enlarged transverse section on the line 2-2 of Fig. 1;

Fig. 3 is an enlarged side view showing the head of the spark plug in partly assembled fonn;

Fig. 4 is a fragmentary axial section of the ignition chamber of a spark plug showing a modified construction embodying my invention;

Fig. 5 is a transverse section on the line 5-5 of Fig. 4; and

Figs. 6 and 7 are axial sections of the studs of Figs. 1 and 4 respectively showing modifications.

The spark plug shown in Figs. 1, 2, and 3 includes an insulator 10 of ordinary construction and a metal body re-enter the spark plug body.

2,843,780 Patented July 15, 1958 2 11. The lower part of the body 11 contains a passage 12 which tapers inwardly to a cylindrical portion which is the ignition chamber 13.

In the lower end of the body 11 is a head 15 consisting of three parts, namely, a disc 15a, a baffle plate 15b, and a central stud 150. As shown in Fig. 3, the head is assembled by forcing the stud 15c into the central bore in the disc 15a to bring the bafile plate 15b over a stem 15d projecting from the disc 15a. When the head has been assembled and the disc 15a forced into an enlarged bore 16 at the end of the body 11, the baflle plate 15b provides a series of helical bafiles forming helical passages from the ignition chamber 13 to jet passages 17 which extend through thedisc 15a. These passages are much more nearly axial and of less cross section than the helical passages between the bafiles.

It is advantageous to join the parts 15a and 15b to each other and to the body 11 by copper brazing or the like to insure good heat conduction.

Electrodes 20, 21 with opposed spherically curved convex faces are located in the passage 13. The electrode 20,is formed at the lower end of the usual conducting rod extending through the insulator, while the electrode 21 is formed by the head of the stud 15c and is larger in diameter than the electrode 20.

The operation of the spark plug which has been described is as follows:

During a compression stroke the explosive mixture enters the spark plug body through the passages 17 and the helical passages between the baflle plates 15b, which produces a swirling mass of gas in the ignition chamber 13. On ignition, the voltage which is applied to the electrode 20 causes a spark to jump' across the center of the gap between the electrodes. The effect of the swirl set up in the ignition chamber during the compression stroke is to draw the spark from a central portion in the gap to the edge portion thereof, increasing its length and decreasing its amperage. This important effect has been observed both directly in a test spark plug provided with a window and indirectly by measurement of the amperage of the current flowing to and across the spark gap. The lengthening of the spark reduces its heating effect on the electrodes and also the danger of pitting the electrodes. It also makes the ignition more effective, especially when starting The gas ignited in the chamber 13 is forcibly ejected into the cylinder through the jet passages 17 at high velocity to ignite the gas in the cylinder. On explosion of the cylinder gases, the pressure in the cylinder becomes greater than the pressure within the body of the spark plug, and for a brief interval hot burnt gases start to The fact that the jet passages 17 are out of line with the helical passages between the bafiles 15b retards return flow of the hot combustion gases. Such hot gas as: does enter is cooled by expansion as it passes from the jet passages 17 into the helical passages of greater cross-section. In these two ways the heat which can be delivered to the electrodes by the hot gases in the cylinder is reduced to a minimum.

Thus, in two diflierent ways the construction acts to increase the life of the electrodes.

In the modified construction shown in Figs. 4 and 5, the head 15 is replaced by a head 25 consisting of a thick disc carrying a central stud 250 which forms a lower electrode 21a similar to the electrode 21.. In this case, inclined tangentially arranged bores 26 in the disc 25 extend from the ignition chamber 13 to smaller, nearly axial jet passages 27. It is apparent from Figs. 4 and 5 that, while the bores 26 are made straight for convenience in construction, they are in a position in which they approximate the turns of a helix. The jet passages 27 extend beyond the points at which the inclined passages 26 open into them, thus providing pockets 28 which retard the entrance of hot burnt gases from the cylinder.

The operation of the modified construction shown in Figs. 4 and'5 'iss'imi'lar to'that of the first construction described.

In the modificationshown in Fig. 6, a small axial bore 3.0 extends through the stud 150 to provide a small passage from the spark. gap space to the cylinder. The .gas which enters the ignition space through this passage during the compression stroke has. two desirable effects: (1) It 'eflects a perfect scavenging of the ignition space and (2) it assists the swirling gases in the ignition chamber in ;moving the spark .away from central position and lengthening it during the ignition. I

In the modification shown in Fig.7, a small passage 31 in the stud 25c connects the spark gap space with the end portion of the ignition chamber. During the compression stroke the swirl of the gases in the ignition chamber causes a suction at the upper end of this passage so that gas flows through this passage to the gas space. The desirable etfects of this flow are similar to those described in connection with Fig. 6.

What I claim is:

1. In a spark plug, a pair of axially arranged electrodes having opposed convex faces providing a spark gap which is shortest on the axis of the electrodes and increases in length towards the periphery of the electrodes, and means for causing gas to swirl about the 'axis of the electrodes, so that a spark initiated in the shortest portion of the gap at the axis of the electrodes is drawn laterally away from the axis increasing the length of the spark and decreasing the amperage of the current across the gap.

2. A spark plug having a body containing a tapering passage and an ignition chamber at the smaller end of its tapering passage, a pair of electrodes positioned axially in the ignition chamber and having opposed convex faces providing a spark gap which is shortest on the axis of the electrodes and increases in length towards the periphery of the electrodes, and a head at the end of the ignition chamber containing helical passages for causing gas drawn into the ignition chamber to swirl about the axis of the electrodes, so that a spark initiated in the shortest portion of the gap at the axis of the electrodes is drawn laterally away from the axis increasing the length of the spark and decreasing the amperage of the current across the gap.

3. The spark plug of claim 1 Which includes means for causing gas to enter the center of the space between the electrodes.

4. The spark plug of claim 1 which includes an ignition chamber housing the electrodes and having a head at one end containing helical passages, said head and one of the electrodes containing a small axial passage leading from the outer side of the head to the center of the gap space between the electrodes.

5. The spark plug of claim 1 in which one of the electrodes contains a small passage extending from the center of its convex surface and opening through its side.

References Cited in the file of this patent UNITED STATES PATENTS 1,320,115 Bloomhutf Oct. 28, 1919 1,454,516 Lee May 8, 1923 1,495,952 Delisle May 27, 1924 1,555,718 Schroeder Sept. 29, 1925 1,929,748 Little Oct. 10, 1933 1,930,003 Erny Oct. 10, 1933 2,008,298 Woods-Humphery et al. July 16, 1935 2,100,320 Browning Nov. 30, 1937 2,127,512 Harper, Jr. Aug. 23, 1938 2,127,513 Harper, Jr. Aug. 23, 1938 

